Re: [Libguestfs] [v2v PATCH v2] output/create_libvirt_xml: relax VCPU feature checking for "qemu64"

On Fri, Jul 22, 2022 at 09:36:27AM +0200, Laszlo Ersek wrote: > When the source domain doesn't specify a VCPU model ("s_cpu_model" is > None), and the guest OS is assumed to work with the default VCPU model > ("gcaps_default_cpu" is true), we don't output any <cpu> element. In that > case, libvirtd augments the domain config with: > > [1] <cpu mode='custom' match='exact' check='none'> > <model fallback='forbid'>qemu64</model> > </cpu> > > where the @check='none' attribute ensures that the converted domain will > be launched, for example, on an Intel host, despite the "qemu64" VCPU > model containing AMD-only feature flags such as "svm". > > However, if the source domain explicitly specifies the "qemu64" model > (mostly seen with "-i libvirt -ic qemu://..."), we presently output > > [2] <cpu match='minimum'> > <model fallback='allow'>qemu64</model> > </cpu> > > which libvirtd completes as > > [3] <cpu mode='custom' match='minimum' check='partial'> > <model fallback='allow'>qemu64</model> > </cpu> > > In [3], cpu/@match='minimum' and cpu/model/@fallback='allow' are both > laxer than @match='exact' and @fallback='forbid', respectively, in [1]. > > However, cpu/@check='partial' in [3] is stricter than @check='none' in > [1]; it causes libvirtd to catch the "svm" feature flag on an Intel host, > and prevents the converted domain from starting. > > The "qemu64" VCPU model is supposed to run on every possible host > <https://gitlab.com/qemu-project/qemu/-/blob/master/docs/system/cpu-models...;, > therefore make an exception for the explicitly specified "qemu64" VCPU > model, and generate the @check='none' attribute. > > Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2107503 > Signed-off-by: Laszlo Ersek <lersek(a)redhat.com&gt; > --- > > Notes: > v2: > - make the attribute dependent on "qemu64" [Rich] > - retrofit the commit message > > v1: > - https://listman.redhat.com/archives/libguestfs/2022-July/029504.html > > output/create_libvirt_xml.ml | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/output/create_libvirt_xml.ml b/output/create_libvirt_xml.ml > index 531a4f75bf3e..bd01304df674 100644 > --- a/output/create_libvirt_xml.ml > +++ b/output/create_libvirt_xml.ml > @@ -192,6 +192,8 @@ let create_libvirt_xml ?pool source inspect > List.push_back cpu_attrs ("mode", "host-passthrough"); > | Some model -> > List.push_back cpu_attrs ("match", "minimum"); > + if model = "qemu64" then > + List.push_back cpu_attrs ("check", "none"); > (match source.s_cpu_vendor with > | None -> () > | Some vendor -> ACK - but see also: https://listman.redhat.com/archives/libguestfs/2022-July/029520.html Rich.